You can’t improve what you don’t measure. But what if you’re measuring the wrong thing? There is a dizzying array of metrics and tools to measure website speed, many of which are contradictory, some of which are ideal for static content, and others for dynamic content/database-driven websites.

At the same time, modern web technology has enabled a new breed of app-like websites, such as eCommerce progressive web apps (PWAs) and single-page applications (SPAs), which deliver amazing page load times. However, these websites appear to load slower than they actually are when measured by most of the popular website speed metrics, which were created to measure legacy, multiple-page websites. As a result, you could be missing out on critical business growth simply because you are using the wrong tools or metrics to measure website speed.

If you are running a revenue-generating eCommerce website, picking the right metrics to measure may be the most important way to align your teams around the goal of creating a fast loading site.

This article will tell you exactly what speed metrics and tools to use to measure eCommerce page load times in 2019/2020 for maximum revenue impact. Consider this your 'how-to' cheat sheet.

Four tips to measure website performance for maximal revenue impact

Here are four simple tips to filter out the noise and get you going:

1. The single best metric is Largest Contentful Paint (LCP)

Did you know waiting for a page to load creates the same psychological discomfort as watching a horror movie? You can significantly decrease the risk of scaring customers away by measuring and optimizing for the right perceptual metrics.  

When the largest image above the fold has loaded (i.e. on a homepage, category page, or product page), the more a consumers perceives a page as fully loaded and are more likely to make a purchase. A few page load metrics measure this milestone, including Last Painted Hero (LPH), Largest Image Rendered (LIR) and Largest Contentful Paint (LCP), however LCP has become the standard metric per Google's 2020 Page Experience Update. LCP is one of three Core Web Vitals, and is now included in SpeedCurve.

LCPs up to 2.5 seconds are considered fast and rank in the 75th percentile for this metric. Optimizing for this metric has been found to be better correlated with eliminating the psychological stress associated with slow page load, than Time To Interactive (TTI), First Meaningful Paint (FMP) and other common metrics.

Measure your website performance in Lighthouse and aim for an LCP in under 2.5 seconds. 

SpeedCurve and Google do a great job explaining why these are the best metrics to measure website speed.

*Note: We've updated this section of the post to reflect Google's Core Web Vitals. Previously, we listed Last Painted Hero (LPH) as the best metric, which measures when the last piece of critical content is painted. For eCommerce websites, this is typically when the largest image is rendered. However, Speedcurve has been updated, offering LCP in the monitoring dashboard, emphasizing its standardization.

2. Measure browsing speed, not only the first page load time

Most benchmarks focus on the first page load of a website. While that metric is very important, especially now that Google ranks faster sites higher in its search results, most shoppers spend much more time waiting for pages to load while browsing through products and categories. In fact, Wolfgang Digital found that the average shopper spends just over 3 minutes browsing through six pages on an eCommerce site, with 21% of this time spent waiting for pages to load.

Fast first load times increase search ranking and thus organic traffic, while faster browsing transitions improves conversion rates. Optimizing and measuring both is critical. Fortunately, two free tools can be configured to measure browsing speed: WebPageTest.org for synthetic tests (email go@moovweb.com to get test scripts that show you how) and Firebase for real-user measurements (RUM).

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3. Use 4G settings, not 3G to measure speed

Many tools still default to measuring website performance under simulated 3G conditions. But according to the Chrome User Experience Report (CrUX), the most comprehensive RUM data in the market, most consumers are probably on 4G, even outside the US. The pitfall of using 3G is that you may end up optimizing different things and slowing down or making little improvement to your 4G speed, which will actually hurt your overall revenue.

Measure your website speed through 4G settings

4. Use both synthetic and real user measurement (RUM)

Synthetic tests determine the performance of a website by simulating a page load times inside a testing tool and can run "on demand" whenever you need them. RUM measures page load speeds actually experienced by real shoppers on your website, but you have to wait to aggregate these metrics from the browsing activity of your site visitors. Both must be tracked. Synthetic tests are important as part of your continuous integration and build processes so that you can ensure no release causes your site speed to regress. RUM is the ultimate measure of what site speed your shoppers’ experience.

Bottom Line

In late 2019, it is possible to create instant eCommerce websites with median LCP as measured by RUM on the mobile web of 0.3 seconds (both first loads and browsing transitions), which is literally the blink of an eye.

First-page load times can be delivered in 0.8 to 1.5 seconds using server-side rendering, and 0.2 to 0.3 seconds when using Accelerated Mobile Pages (AMP) which are pre-fetched by Google’s search results page.

Don’t leave money on the table, schedule a consultative conversation to learn how the Moovweb XDN can help your company achieve sub-second page load times, increase organic traffic by an average of 32.1%, and lift conversions by 15-30%.